Miniature radiating electrocardiograph



July 20, -1965 .|.IF. wEsTERMANN MINIATURE RADIATI-NG ELECTROCARDIOGRAPHINVENTOR ATTORNEYSy Filed June 21, 1961 @g BY fm, WML-4 United StatesPatent O 3,195,535 MHNATURE RADIA'HNG ELECTRO- CARDHOGRAPH .oseph i?.Westermann, Abington, Pa., assigner, by mesne assignments, to UnitedAircraft orporation, a corporation of llielaware Filed .lune 21, 1961,Ser. No. 11%,605 3 Claims. (Ci. 12S- 2.06)

This invention generally relates to electrocardiographs and isparticularly concerned with miniature battery powered electrocardiographapparatus adapted to be carried by or attached to the patient and tocontinuously monitor the patient and transmit the information obtainedover radio waves to a remote receiving station.

It is accordingly a principal object of the invention to provide a radiotransmitting electrocardiograph apparatus for providing dynamicmeasurements of the patient while the patient is experiencing thestresses of normal Work and other activities.

Another object of the invention is to provide a portable radio beamgenerating electrocardiograph adapted to be Worn by the patient wherebythe patient is completely unrestrained in his activities whilediagnostic measurements of the heart are being made.

A further object is to provide such apparatus in miniature size andweight adapted to be easily carried or worn by the patient withoutimpeding his normal activities or body exercises and without beingexternally observable by others so as to cause discomfort orembarrassment to the patient.

A more specific object is to provide a radio electrocardiographtransmitter system comprised completely of battery powered transistorcircuitry that is adapted to be worn in close proximity to the patientsbody, yet is substantially unalfected by body heating or variations involtage of the powering battery.

A still further object is to provide such a system for transmitting afrequency modulated carrier radio beam proportional to the patientscardiac responses that is extremely stable in operation despitevariations in temperature, battery voltage, and other externalinlluences or body generated extraneous signals.

Other objects and additional advantages will be more readilycomprehended by those skilled in the art after a detailed considerationof the following specification taken with the single accompanyingdrawing illustrating, partially in block diagram form and partially inelectrical schematic diagram form, one preferred embodiment of theinvention.

Referring now to the single drawing, there is shown one complete radioelectrocardiograph apparatus adapted to be worn by the patient and totransmit by means of a frequency modulated radio Wave, theelectroeardiograph data to a remote radio receiver (not shown) that maybe located at `a hospital, a doctors oflice or elsewhere at somedistance from the patient.

As shown, the system generally includes a pair of electrodes or sensors8 and 9, illustrated within dotted enclosure 10, adapted to be attachedto closely spaced positions on the patients body, a pair of smalldiameter flexible electrical conductors 11 and 12 for connection to theelectrodes for the purpose of conveying the electrical body generatedsignals, and a complete radio transmitter 3,195,535 Patented July 20,1965 ICC and antenna system, including components generally designated16, 1S, 2t) and 21 for responding to the desired signals from the bodyand for producing and radiating a frequency modulated radio wave toconvey the cardiac information to a remote receiver (not shown).

All of the apparatus depicted in the drawing with the exception of theelectrodes 8 yand 9 and the connecting wires 11 and 12 is adapted to becontained within a single miniature housing approximating the size of acigarette package whereby this housing may be easily concealed in apocket of the wearers clothing or suitably strapped to the body withoutbeing externally noticeable to others. The apparatus is also adapted tobe completely powered for operation by means of a single small secondarybattery, such as a cadmium nickel battery 57 or other as is presentlyavailable on the open market.

According to the invention, the body electrodes S and 9 are adapted tobe continuously attached to the patients body for a relatively longperiod of time and to maintain low electrical resistance coupling to thebody despite various changes in body movement and body curvatureoccurring while the patient is performing a variety of activities. Thepreferred electrodes are also quite small in size and easily attached tothe body without awkward 7 straps or fastening means whereby they may beworn by the patient without impeding or interfering in any substantialmeasure with his activities, or causing him any discomfort. A preferredelectrode construction providing these characteristics is disclosed in acopending application 4of Richard Berman and Bernard Schwartz, SerialNo. 116,586, led June 12, 1961, and assigned to the same assignee, nowPatent No. 3,085,577.

The low voltage level signals being obtained from these electrodes aredirected over iiexible insulated conductors 11 and 12, and throughsuitable low frequency pass electrical lters in each conductor line,including capacitor 13 in line 11 and inductor 14 and capacitor 15 inline i2, to a pair of separate input terminals of a differentialamplifier 16. In the differential amplifier 16, the pair of low voltagelevel electrode signals are filtered and combined in such manner as toeliminate any extraneous cornmon mode signal that is transduced by bothelectrodes in common, thereby to produce a single signal representingthe desired cardiac information. This single signal is ampliiied by aratio of about 200 to 30() to one and thence conveyed over an input line17 to frequency modulate the preferred radio transmitter shown withinthe dotted enclosure designated 18.

Due to the fact that the `complete miniature transmitting system isadapted to be battery powered by a small secondary battery and isadapted to be strapped to or carried close to the patients body, it issubjected to variations in the voltage of the battery as well as changesin temperature resulting from body heat and ambient temperaturevariations. For `this reason, the differential amplifier 16 iscompensated t-o prevent such variations from affecting thecharacteristics of the amplified cardiac signals produced over line 17since otherwise, the transmitted signals would be subject to error andwould not accurately reflect the condition of the patient. One preferreddifferential amplifier 16 providing the functions described and beingcompensated against such extraneous influences is disclosed in thecopending application of Lyman Bethke, Serial No. 115,711, tiled lune 8,1961,

lated carrier is then directed over output line 19 toV alow pass filterto remove any extraneous higher frequency as will bev of eliminating anyextraneous signals" from entering the i transmitter ,18. Thecapacitorv22 is aA high capacity signals and is then passed outwardlyover line 21 leading Y to la radiating antenna means whereby the, radiolbeam may be propagated to a remote receiving and monitoring station (notshown). Y

At the remote receiving station, which may'belocated at adistanthospital, doctors .office .or the like, the frequency modulatedradio beam is received and Vdetected to reproduce the intelligencesignal and enable the heart wave signals to be recorded and displayedcna recording oscilloscope or other recorder as is well Vknown intheart.

It is `preferred to minimize the number of external leads and connection`wires so that the apparatus may be installed and put into use bydoctors and medically trained technicians without the need for specialelectronic training Ain the use of the equipment. For vthis reason theexternalfexible connector `12, interconnecting theV body electrode 8with the differential amplifier 16, is also preferably employed as` theradiating antenna for the system by being connected to the radio outputline' 21'.'

trodes 8 and 9 to thek miniature lhousing forthesys'tem` e'lectrolytictype capacitor for providing a low reactance to the passage of the`desired low frequency intelligence signals while at the same timeblocking the passage of any extraneous direct current signals that maybe carried over line 17. The inductor 24, on the other hand,V provides alarge reactanceY to prevent the passage of any undesired higherfrequency signals to and from line 17 to the transmitter butpermitsthelower frequency intelligence signals to pass through to the transmitter.Since the overall circuit is adapted to be miniaturized in size, it ispreferred that the capacitor 22 be a titanium electrolytic lcapacitorfor providing-the desired high capacity neededtand being obtainable in avery smallsize unit.

Y After beingfilter'ed, the Vintelligencesignal is applied across avoltagev'ariable capacitance diode V26 whose alternating currentcapacitance is .varied in proportion to theV amplitude of the lowfrequencyintellligence signal. This variable capacitance diodeeffectively functions `as part of,the..modulator whereby the variationsin the capacitance of this `diodef26 are employed to vary the frequencyVof the oscillatoras will bemore fully dis- `cus-sed below. l l

The transistor in the first stage of `the transmitter isf connected'inaHartleyoscillator type configuration with its base electrode beingconnected in series-with a piezoelectric crystal 31 to theupper terminalofl a feedback tank circuit,.including capacitor 28and inductor 29, and

with `a tap or terminal on inductor 29 being connected through aresistor34 to the emitter electrode.y The collector electrode ,oftransistor 35 is Vconnected to the upper tive terminal vof the battery57 and alternating current to serve as both Yinput leads from theelectrodes andas a radiating antenna for the system. Y n l v Thepreferredftran'smitter shown within the dotted'` enclosure designated 18is preferably comprised of three` signal over line 17 to produce avariable frequency al-j ternating current signal, in the lowradiofrequency brand, across its output tank circuit, including parallelconnected capacitor 364 4and inductor 37. t

In the second stage, this` variable frequency radio signal isproportionally lincreased in frequencyby a factor coupled to thepositive terminal lat groundv through a capacitor39. It is Vto be notedatthis point, however, that the complete portablesystem is adapted to becarried by thepatient andnis not connected to actual ground at anyposition, and that the ground symbols on Vthe drawing,

t therefore, signify only the positive terminal of the portable of abouttwo'to one to double the frequency ofthe.

oscilla-tor, and in the third stage,` the resulting radio signal isfurther multiplied in frequency by a factor of.

The purpose vof providing this rather high ratio of frequencymultiplication in the transmitter is vto provide a wide range offrequency devi-ation inthe output radio signal Ain response'to Atheincoming intelligence signals" originating frorn the electrodes Stand 9,or in other words, to provide a highly sensitive transmitting systemwherein a small change'in the amplitude Mof the Velectrode signalsproduces a relatively large variation in the frequency of thepropagatedradio beam.

Returning vnow to the drawing and tracing through the prefenredvtransmitter circuit 18, the incoming intel-'- ligence signal from` theamplifier V16 and vover line 17 is first directed through a filterincluding a series connected capacitor 22,resistor 23 and inductor 24for the purpose battery.` It will also be notedpthat throughout lthetransmitter, alternating current by-pass capacitors 39,` 46 and 55are-employed to prevent the alternating current signals Y frompassing'through the battery terminals.

' Returning to the first stage oscillator, the lower terminal of theinput tank circuit is alternating current coupled toA the lower terminalof the output tank'circuit through capacitor 39 andthe direct currentbattery potentialis applied across these terminals. Forproviding directcurrent biasing of the base electrode, avoltage divider comprisingresistors 32 and 33-,isl energizedacross the terminals of the batteryand the junction of .these resistorsl isV connected to the baseelectrode ofY transistor 35. y

Inoperation, the resonant frequency of the tank circuit comprising thervoltage variable diode capacitor 26,l fixed capacitor 28and inductor29, operatingwith the crystal 31, normally determinesthe Ystablevfrequency of oscillation Vof the first stage and this oscillatingsignal, together with its harmonics, is produced across the `output tankcircuit comprising capacitor 36 and inductor 37. The'incoming lowfrequency intelligence signal over v,line 17 'varies the capacity ofthevoltage variable diode 26 and, therefore,

t the oscillator signal from -being transmitted backwardly` changesV theresonant frequency offthis tank circuit thereby to vary ther oscillationfrequency. This xlowfrequency modulating signal over line 17 is blockedfrom reaching the ybase electrode of transistor .35 by thecouplingcapacitor 27 which serves to couplethe higher Voscillatorfrequency to the variable capacitordiode 26 but decouples the modulatingsignal fromvtransistor 35. The series connected inductor 24 on the otherhand prevents to the amplifier 16.

Thus the oscillator frequency in the first stage is varied in proportionto the amplitude of the incoming intelligence signal over line 17. Thisvariable frequency oscillator signal is produced across the output tankcircuit, comprising capacitor 36 and inductor 37, which tank circuit istuned to resonance over a narrow band at the second harmonic frequencyof the oscillator. The variable oscillator signal is thus doubled infrequency at the output of the first stage.

To provide an oscillator signal that is rich in the higher frequencyharmonics, a resistor 34 is placed in the emitter circuit of transistorwhereby the oscillator stage functions in the class C region to providethe necessary harmonics for the frequency multiplication stages.

Since the transistor 35 is subject to variation with temperature changeas may result from the body heat of the patient or other externaltemperature variation, the present invention provides compensation forthis effect to insure that the oscillator frequency remains stable andvaries only according to the intelligence signal as desired. Thiscompensation is provided by employing a capacitor 28 in the tank circuitpossessing a negative temperature coeicient whereby its capacitydecreases with increase in temperature. Since this capacitor 28 servesas one parameter in controlling the frequency, and it functions inopposition to the temperature changes in transistor 35, the oscillatorfrequency is stabilized against undesired variations due to temperaturevariations.

From the output tank circuit of the first stage oscillator, thefrequency modulated radio signal is coupled to the second stage by asecondary winding 3S that is inductively coupled to inductor winding 37,as shown. From the secondary winding 38, the radio signal passes througha coupling capacitor 4f? and is applied between the emitter and baseelectrodes of transistor 43. The transistor 43 is connected in a commonbase configuration, with the base electrode being connected directly tothe positive terminal of the battery and the collector electrode beingenergized by the negative terminal thereof through a resonant tunedcircuit comprising a capacitor 44 shunted by an inductor winding 45.Direct current biasing is applied between the base and emitter by meansof a series connected resistor 4Z and inductor 41 connecting theseelectrodes, with the inductor #il being in circuit to prevent the radiosignal from affecting the direct current biasing of the transistor.

This common base configuration of the second stage transistor 43'provides maximum amplification at the high radio frequency involved dueto the more favorable interelectrode capacities of the transistor beingprovided with the transistor in this configuration. it also providesoptimum stability despite variation in the potential of the batteryvoltage as well as improved frequency response for the frequencyvariable radio signal being conveyed.

The output tuned circuit comprising capacitor d4 and inductor 4S is maderesonant at the third harmonic frequency to provide an additionalfrequency multiplication of the radio signal.

rEhe third or final stage of the transmitter, and including transistor5l., is essentially in the same circuit conguration as is the secondstage with the transistor 51 being connected in -a common baseconguration to provide optimum gain compatible with the desiredfrequency response and stability of the circuit despite variations .inthe potential of the battery. The input and output circuits thereof areprovided with tuned tank circuits to provide additional frequencymultiplication of the radio signal as is desired. Thus the output radiosignal being produced by the transmitter over line 19 is a frequencymodulated radio signal having a wide range of frequency deviation inproportion to the cardiac intelligence signal obtained from theelectrodes.

As generally discussed above, the frequency modulated radio signal overline 19 is then passed by a low pass filter Ztl to remove any extraneoushigher frequency noise and finally directed over line 21 to theradiating antenna input connecter 12 Where it is propagated as a radiobeam to a remotely located frequency modulation receiver.

Although but one preferred embodiment of the invention has beenillustrated and described, many variations may be made by those skilledin the art without departing from the spirit and scope of the invention.Accordingly, this invention should be considered as being limited onlyby the following claims.

What is claimed is:

1. In a portable self-contained radio electrocardiograph apparatusadapted to be completely carried hy the patient and free of externalelectrical wiring interconnecting the patient with a fixed location formonitoring the patients heart characteristics in a dynamic fashion whilethe patient is subjected to stresses encountered by unrestrainedactivity, ransducer electrodes adapted to be bonded to the patients skinand being iiexible to maintain low resistance contact with the samelocation on the body despite variations in body curvature, andtransmitter means producing a carrier radio-frequency responsive toelectrical signals obtained from the electrodes to produce a frequencymodulated ultra high frequency radiation to be detected at a remotelocation, said transmitter means comprising a battery, a radio frequencyoscillator powered by the battery, and a housing containing saidoscillator and battery and adapted to be carried by the patient duringunrestrained activity in intimate heat transferring relationship withthe patients body and means for stabilizing said transmitter means toprevent heating by bo-dy temperature and variations in battery potentialfrom producing spurious variations in the radiation, said stabilizingmeans including a temperature sensitive electrical component in saidoscillator for varying the oscillator frequency in opposition to thechange normally produced by heat.

2. ln a self-contained electrocardiograph system adapted to becompletely carried by the patient and having no external electricalwiring interconecting the patient with a fixed location, smallelectro-des for attachment to the patients skin and providingsubstantially constant low electrical resistance with the same skinlocations despite variations in body curvature with unrestrainedmovement of the patient, and a battery powered radio transmitteroperating in the ultra high frequency bandwidth, said transmitter beingmodulatable according to the electrode produced signals to vary itsfrequency of radio transmission, and means for compensating saidtransmitter against spurious variations, said transmitter including alower frequency crystal controlled oscillator and frequency multiplierstages for proportionately increasing the frequency of the oscillatorfor transmission in the ultra high frequency bandwidth, and means forvarying the frequency oflthe oscillator according to the electrodeproduced signa s.

3. in a self-contained electrocardiograph system adapted to becompletely carried by the patient and having no external electrical wireinterconnecting the patient with a fixed location, small electrodes forattachment to the patients skin and providing substantially constant lowelectrical resistance with the same skin locations despite variations inbody curvature with unrestrained movement of the patient, and a batterypowered radio transmitter operating in the ultra high frequencybandwidth, said transmitter being modulatable according to the electrodeproduced signals `to vary its frequency of radio transmission, and meansfor compensating said transmitter against spurious variations, saidtransmitter including a lower frequency crystal controlled oscillatorand frequency multiplie-r stages for proportionately increasing thefrequency of the oscillator for transmission in the ultra high frequencybandwidth, and means for varying the frequency of the oscillatoraccording to the electrode produced signals, said means including avoltage variable capacitor diode.

eferencc-s on following page) Y References Cite by Ehe Examiner y Y 'Y V3,051,896 8/ 62 Begani i.- 324-71 2756741 Ugmsm PATENTS ,128 '2 05 jiif?? Y:23:11:31:*S 2,827,040,l v3/58 GillrfI-ln- 128:2:05 5 Y .QTHERREFERENCES 2,484,992 g/58 pigeon Y1259.105V v Barr, The M111tary Surgon,February 1954, pgs. 79-83.

i j: 'i RICHARD A- GAUDE'T Pffmafy Emmen 2,981,911 4/ 61 Warnick12S-2.05 XR RICHARD ,.T.V HOFFMAN, JORDAN FRANKLIN, 3,029,808 4/62 Kagan12S-206 1() A Y -Y Y 1 Examiners. Y

1. IN A PORTABLE SELF-CONTAINED RADIO ELECTROCARDIOGRAPH APPARATUSADAPTED TO BE COMPLETELY CARRIED BY THE PATIENT AND FREE OF EXTERNALELECTRICAL WIRING INTERCONNECTING THE PATIENT WITH A FIXED LOCATION FORMONITORING THE PATIENT''S HEART CHARACTERISTICS IN A DYNAMIC FASHIONWHILE THE PATIENT IS SUBJECTED TO STRESSES ENCOUNTERED BY UNRESTRAINEDACTIVITY, TRANSDUCER ELECTRODES ADAPTED TO BE BONDED TO THE PATIENT''SSKIN AND BEING FLEXIBLE TO MAINTAIN LOW RESISTANCE CONTACT WITH THE SAMELOCATION ON THE BODY DESPITE VARIATIONS IN BODY CURVATURE, ANDTRANSMITTER MEANS PRODUCING A CARRIER RADIO-FREQUECY RESPONSIVE TOELECTRICAL SIGNALS OBTAINED FROM THE ELECTRODES TO PRODUCE A FREQUENCYMODULATED ULTRA HIGH FREQUENCY RADIATION TO BE DETECTED AT A REMOTELOCATION, SAID TRANSMITTER MEANS COMPRISING A BATTERY, A RADIO FREQUENCYOSCILLATOR POWERED BY THE BATTERY, AND A HOUSING CONTAINING SAIDOSCILLATOR AND BATTERY AND ADAPTED TO BE CARRIED BY THE PATIENT DURINGUNRESTRAINED ACTIVITY IN INTIMATE HEAT TRANSFERRING RELATIONSHIP WITHTHE PATIENT''S BODY AND MEANS FOR STABILIZING SAID TRANSMITTER MEANS TOPREVENT HEATING BY BODY TEMPERATURE AND VARIATIONS IN BATTERY POTENTIALFROM PRODUCING SPURIOUS VARIATIONS IN THE RADIATION, SAID STABILIZINGMEANS INCLUDING A TEMPERATURE SENSITIVE ELECTRICAL COMPONENT IN SAIDOSCILLATOR FOR VARYING THE OSCILLATOR FREQUENCY IN OPPOSITION TO THECHANGE NORMALLY PRODUCED BY HEAT.